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Introduction

The entire Himalaya region is highly vulnerable to the impacts of global warming and forest ecosystem can be seriously impacted in these changes. Phenological events of the plants are good indicators of climate differences^1,2.Phenology involves precise documentation of timing and duration of different phenological events at species level, their interrelations and possible causal links between environmental variables and phenology³,各种物候事件such as leaf-expansion, abscission, flowering, bud-burst, fruiting, seed dispersal and germination of Himalayan species all take place in due season^3,4. Phenological studies are as important to understand the species interactions and community function because each phenological events of each species occurs in its own calendar slot⁵. Fruiting must wait upon flowering; seed dispersal cannot precede fruiting even an individual flower undergoes a sequence of events^4,6.

A number of studies in different parts of the world indicate that global warming of last three decades has advanced by a few days several spring time activities such as leaf production flowering and fruiting in plants^7、8. The observed change may be a positive sign because species are apparently adapting to changing climatic conditions, or they may be negative sign because they show that climate change is indeed impacting living systems⁹.A number of studies have convincingly demonstrated that plants are already responding to climate change with earlier leafing, flowering and leaf drop^10,12. It is an important component for predicting how species will respond to global warming and increasing drought stress in recent scenario of changing climatic patterns¹³.The most significant ways by which trees can react and cope with rapid environmental change could be adjustments of phenological pattern, allowing trees to persist in their environment^14,15.Phenological phases are closely linked with temperature, rainfall and photoperiod and adversely affect the pattern of phenology in same or different species on a small region.A number of evidenceshave been reported by various researches that phenophases of several species changed by changing climatic patterns. The present work focuses on the documentation of the phenological events and compared with earlier studies to find the shift the phenophases in last three decades and effect of climate change on phenological events ofsal, chir-pine and banj oak dominated forests in Nainital forest division of Kumaun Himalaya.

Material and Methods

The study sites were selected across an altitudinal transect located between 413 and 2345m elevation (between 29⁰18^/and 29⁰24^/N and 79⁰19^/and 79⁰30^/E) in sal, chir-pine and banj oak dominated forests in Nainital forest division of Kumaun Himalaya. In the sal dominated forestShorea robustaRox(Sal) andMallotus philippinensis(Lam.)Muell.Arg (Rohini) in chir-pine dominated forestPinus roxburghiisarg(Chirpine) andMyrica esculentaThumb(Kaphal) and in Oak dominated forestQuercus leucotrichophoraA.camus(Banj Oak) andRhododendron arboreumWall(Buransh) were selected for detailed phenological observation (Table 1).

Table 1: Physiographic Features of selected Forests Studied Sites.

In sal forest the average annual precipitation was 1201mmandmean annual temperature was 23.4⁰C with mean minimum temperature was 7.5⁰C in the months of December and mean maximum temperature was 35.5⁰C in the months of June. In oak and pine forest average annual precipitation was 2258mm of which two third occurred during rainy season (mid-June to mid-September. Mean annual temperature was 15.2⁰C with mean minimum temperature was 4.6⁰C in the months of January and mean maximum temperature was 25.9⁰C in the months of June.

Irrespective of site 30 individual trees of each selected species (one dominant and one under canopy species) were marked forS.robusta,M. philippinensis,P. roxburghii,M. esculenta,Q. leucotrichophoraandR. arboreumover a 2.0 ha area. The phenological observations were made at 15 days interval during low activity period and weekly in the periods of high phenological activity^4,16. Phenological records were made for four phenophases, viz., leafing, leaf drop, flowering and seed fall for all studied species for a two-year period and compared with earlier studies to find the shift in phenological events in last three decades.

Results and Discussion

Shorea Robusta

Across all the sites the leaf fall in S. robustastarted from March 2^ndweek and was complete by the end of April. Flower bud break started from March 2^ndweek and flowering was in <10% trees after 2-3 days of flower bud break. Flowering had peaked in the 4^thweek of March (75% trees had flowered). New leafing started after one week of floral bud opening and by the April end trees had maximum new leafing (95%). However, in seedlings and saplings it continued till July end. Seed fall started from June first week and almost all fruits had fallen after the torrential rain in the third week of June (Fig.1 and 2).

Mallotus Philippinensis

In this species the leaf fall started in the 2^ndweek of June and was complete in August 2^ndweek. New leaves started appearing from May 3^rdweek and leafing was completed in August 1^stweek. However, in saplings and seedlings new leaves appeared after July during August and September. Flowering started from September end and was completed in the mid of November. Fruiting commenced from the beginning of December and seed fall was complete by the 3^rdweek of April (Fig.1 and 2).

Pinus Roxburghii

Needle bud enlargement started from February end and was complete by the 2^ndweek of March. Needles had attained their maximum length ranging between 14.3cm to 17.1cm by May end. Leaf fall started from March last week and was over by May 2^ndweek. Seed dispersal commenced from April 2^ndweek and was completed by June 2^ndweek(Fig. 1 and 2).

Myrica Esculenta

Leafing started from April 2^ndweek and was completed by May end when >95% trees and saplings had leafed. Leaf fall started from June 2^ndweek and continued till 2^ndweek of July. Seed fall was observed from April end and was completed by 3^rdweek of May only occasional trees had fruits. Only a few trees (10%) ofM. esculentahad seeds, and it may be concluded that year as a lean seed year. Male flowers appear from August end and flowering was complete by October end. Maximum flowering was observed between August end and September 2^ndweek when 80% trees had flowers (Fig.1 and 2).

Quercus Leucotrichophora

Seed fall commenced from 2^ndweek of November and seed fall was complete (85%) by January end. Bud bursting started from February end and was completed by March end across all the sites. Leafing started in the 1^stweek of March and was completed in the 1^stweek of April in trees. Leaf fall started simultaneously with bud bursting and continued till April end. Acorn appeared from March 1^stweekand continued to appear till 2^ndweek of April. Seedlings and saplings showed late bud opening, leafing and leaf fall compared to matured trees. Bud bursting was earlier at the disturbed sites(Fig.1 and 2).

Rhododendron Arboreum

Flower bud bursting and flowering started from 1^stweek of February (<5% trees had flowers). However, occasional trees started flowering from February 1^stweek. Flowering peaked in 1^stweek of April (>75% tree had flowered) and was completed by the end of May. New leaves appear after the completion of flowering from May 3^rd周和雨季年底完工。Leaf fall took place round the year but was maximum during the summer months (May-June). Seed dispersal started from February end and all the capsules had opened by mid-March. Leaf longevity of this species is more than 16 months (Fig.1 and 2).

Figure 1: Timing of Phenological Events during Year 1. Click here to view Figure

Figure 2: Timing of Phenological Events during Year 2. Click here to view Figure

We compared the timing of phenological events of present study with the earlier studies of^17,18.In S. robusta when we compared the timing of flowering initiation and completion with earlier studies, we do not find any significant shifts in timing of these phenological events^17,18. There was no perceptible change in the initiation of leaf drop and leaf fall completion in comparison¹⁸. However, the period of leaf flushing has become small by approximately a month in comparison to earlier studies (Table 2). In M. phillippinensis the period of leafing has been reduced by approximately 4-6 week. The period of leaf drop and leaf flushing were similar to¹⁷. In P. roxburghii the time of flowering initiation has become earlier by 4-6 weeks. Similarly, commencement of needle drop was also earlier by 4-5 weeks in comparison to earlier studies (Table 2). In M. esculentathe timing of flowering initiation and completion showed no change in comparison to earlier studies. Leaf flushing initiation was earlier by 4 weeks in both the years whereas leaf drop initiation was delayed by 2 week and completion was same incomparison to earlier studies (Table 2). In Q. leucotrichophora there appear to be no major changes in the timing of flowering and new leaf flushing; however, the period of leaf drop has become extended by 2-3 weeks in comparison to earlier studies (Table 2). In R. arboreum it has reported flowering initiation in January extending up to April¹⁷. Earlier researcher has given more restricted period of flowering February-March for the species¹⁸. In our study flowering commenced from January II week and continued up to May II week in both the years showing more extended flowering period. The period of leaf drop also shows an extended period coupled with leaf flushing (Table 2).

Table 2: Comparison of Changes in Timing of Leaf Drop, Leafing and Flowering in Studied Species with Earlier Studies.

Conclusion

It is apparent from the present study that due to climatic irregularities and temperaturerise the role of temperature would become paramount in controlling/shifting of the phenological events. Many species shifted their flowering time across the worldwide. Global warming could be a primary cause for these changes some other factors also responsible for these changes such as precipitation pattern, soil and water stress, moisture condition andphotoperiod that would be useful to better understand spatial patterns in the sensitivity of phenological responses to temperature. Microclimatic condition alsoresponsible for controlling/shifting the phenological patterns of same or different species.Hence, more detailed investigations at the local level are required to examine the influence of these events in future studies.

Acknowledgements

The authors are thankful to the Director, Graphic Era Hill University, Bhimtal Campus and Head, Department of Forestry and Environmental Science, Kumaun University, Nainital for providing facilities in the department.

Funding Sources

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest

The author(s) declares no conflict of interest.

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